There has been typically used a buckle that detachably engages a plug with a socket in order to couple string members (e.g., belts) in various applications (e.g., clothes, bags, shoes and packages)
Such a buckle requires easy handling for coupling and releasing as well as no accidental release when the buckle is not intended to be released. As a product that satisfies such needs, a side release buckle including a pair of lock arm on both sides thereof has been used.
For instance, a side release buckle disclosed in Patent Literature 1 or 2 includes a plug and a socket, each of which is provided with a belt attachment.
The plug includes a base including the belt attachment and a pair of legs (lock arms) on both sides near the socket. The socket has a hollow cylindrical body, the body including a housing space (cavity) into which the plug is inserted from a plug-facing side of the body. An opening in communication with the housing space is formed on each side of the body of the socket. The plug and the socket can be disengaged by manipulating the legs exposed through the openings with fingers.
In such a side release buckle, the plug and the socket each are integrally formed mainly of a synthetic resin material. Accordingly, while the legs are provided with a predetermined elasticity, the plug, the socket and the belt attachment are provided with a sufficient strength to resist tension of the coupled belts in use.
Further, the hollow socket is reinforced by, for instance, securing a thickness of the body of the socket such that the socket is not excessively deformed (e.g., crush) by press in a top-bottom direction.    Patent Literature 1 JP-A-2006-204911    Patent Literature 2 Japanese Design Registration No. 1323896